Solve a multi-step Problem 6. From 1990 to 2001, the number of airports in the United States increased at a
relatively constant rate of 175 airports per year. There were 19,306 airports in the
United States in 2001.

a. How many U. S. airports were there in 1990?

b. Write an equation that gives the number of U. S. airports as a function of the number
of years since 1990.

c. Find the year in which the number of U. S. airports reached 19,500.